Among the greatest challenges facing AIDS vaccine development is the intrinsic diversity among circulating populations of HIV-1 in various geographical locations and the need to develop vaccines that can elicit enduring protective immunity to variant HIV-1 strains. While variation is observed in all of the viral proteins, the greatest diversity is localized to the viral envelope glycoproteins, evidently reflecting the predominant role of these proteins in eliciting host immune recognition and response that result in progressive evolution of the envelope proteins during persistent infection. In the current application, we have designed novel virus-like particle (VLP) immunogens that can optimize mucosal and systemic Env-specific immune responses for evaluation against protection from heterologous SHIV challenge in rhesus macaques by vaginal exposure (the most common route of HIV-1 transmission worldwide). We have constructed DNA plasmids to express VLPs from SHIV gene sequences where each DNA construct expresses a non-infectious lentiviral VLP from a single DNA plasmid. Each VLP gene insert expresses the gag, pol, env, vpu, tat, and rev gene sequences that are expressed from a cytomegalovirus immediate-early promoter via plasmid DNA. Thus, VLP mRNA splicing and nuclear export will be controlled by viral mechanisms and translated proteins efficiently secrete VLPs from transfected cells. Several safety mutations have been engineered into the backbone of the VLP to match the U.S. Food and Drug Administration guidelines for the use of HIV-1 DNA vaccines for human use. In this proposal, gene inserts expressing SHIV VLPs will be expressed from DNA. In addition, SHIV VLPs will be purified from the supernatant of primate cells transfected with the same DNA plasmids. We propose to construct and characterize a library of SHIV VLP-DNA plasmids, each containing a different CCR5 (RS)-utilizing clade B or clade C envelope glycoprotein of HIV-1. Rhesus macaques will be vaccinated in a prime/boost regimen (DNA prime/particle boost) for the elicitation of both humoral and cellular immunity, and protection from heterologous clade B SHIV challenge will be evaluated. The goals of this proposal are to assess and compare the induction of immune responses between VLP immunogens with primary envelopes to the elicitation of immunity by VLP immunogens with an envelope representing the consensus envelope sequences (clade B or clade C). SHIV-1 VLPs will also be assessed for elicitation of immunity and protection to a heterologous SHIV challenge. The use of a consensus envelope as a native oligomer allows for the comparison of protective immunity elicited by consensus envelopes to that elicited by a mixture of primary oligomeric envelopes that are mismatched to the challenge virus. Finally, the breadth and protective efficacy of immune responses elicted by a SHIV-1 VLP containing an envelope representing the consensus envelope sequence of clade C (Con C) will be evaluated with a clade B SHIV challenge.